We don't have synonyms for spongin yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are spongia, spongio and spongi.
(n) :
A horny, sulfur-containing protein, related to keratin, that forms the skeletal structure of certain classes of sponges. A proteinaceous compound of which the spicules in Demospongiae are composed.
(n) :
A horny, sulfur-containing protein, related to keratin, that forms the skeletal structure of certain classes of sponges. A proteinaceous compound of which the spicules in Demospongiae are composed.